Re: [PATCH] of_pci_irq: Silence bogus "of_irq_parse_pci() failed ..." messages.

[David Daney]

On 09/04/2015 06:14 PM, Frank Rowand wrote:
> On 9/4/2015 12:12 PM, David Daney wrote:
> > From: David Daney <david.daney@xxxxxxxxxx>
> >
> > It is perfectly legitimate for a PCI device to have an
> > PCI_INTERRUPT_PIN value of zero.  This happens if the device doesn't
> > use interrupts, or on PCIe devices, where only MSI/MSI-X are
> > supported.
> >
> > Silence the annoying "of_irq_parse_pci() failed with rc=-19" error
> > messages by making them conditional on !-ENODEV (which can only be
> > produced in the PCI_INTERRUPT_PIN == 0 case).
> >
> > Signed-off-by: David Daney <david.daney@xxxxxxxxxx>
> > ---
> >   drivers/of/of_pci_irq.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/of/of_pci_irq.c b/drivers/of/of_pci_irq.c
> > index 1710d9d..33d242a 100644
> > --- a/drivers/of/of_pci_irq.c
> > +++ b/drivers/of/of_pci_irq.c
> > @@ -106,7 +106,9 @@ int of_irq_parse_and_map_pci(const struct pci_dev *dev, u8 slot, u8 pin)
> >
> >   	ret = of_irq_parse_pci(dev, &oirq);
> >   	if (ret) {
> > -		dev_err(&dev->dev, "of_irq_parse_pci() failed with rc=%d\n", ret);
> > +		if (ret != -ENODEV)
> > +			dev_err(&dev->dev,
> > +				"of_irq_parse_pci() failed with rc=%d\n", ret);
> >   		return 0; /* Proper return code 0 == NO_IRQ */
> >   	}
>
> It is not safe to assume that the functions that of_irq_parse_pci() calls
> will never be modified to return -ENODEV, thus resulting in of_irq_parse_pci()
> returning -ENODEV for a reason other than PCI_INTERRUPT_PIN == 0.

Since the current implementation *only ever* returns -ENODEV for 
PCI_INTERRUPT_PIN == 0, we could just document that behavior, and not 
hack up the APIs by adding a second return channel from the function.

The additional change on top of my patch would be to add a comment 
describing this behavior.

David Daney.



> A more robust solution would be something like:
>
>
> (1) Change of_irq_parse_pci() to _of_irq_parse_pci(), adding an argument and
> use it to report the case of PCI_INTERRUPT_PIN == 0.
>
> static int _of_irq_parse_pci(const struct pci_dev *pdev, struct of_phandle_args *out_irq, int *no_pin)
> {
>
> ...
> 	*no_pin = 0;
> ...
> 	/* No pin, exit */
> 	if (pin == 0) {
> 		*no_pin = 1;
> 		return -ENODEV;
> 	}
> ...
>
>
> int of_irq_parse_pci(const struct pci_dev *pdev, struct of_phandle_args *out_irq)
> {
> 	int no_pin;
> 	return _of_irq_parse_pci(pdev, out_irq, &no_pin)
> }
>
>
> (2) Then the fix to of_irq_parse_and_map_pci() would be:
>
>    +     int no_pin;
> >   	ret = of_irq_parse_pci(dev, &oirq, &no_pin);
> >   	if (ret) {
> > -		dev_err(&dev->dev, "of_irq_parse_pci() failed with rc=%d\n", ret);
> > +		if (!no_pin)
> > +			dev_err(&dev->dev,
> > +				"of_irq_parse_pci() failed with rc=%d\n", ret);
> >   		return 0; /* Proper return code 0 == NO_IRQ */
> >   	}
>
>
> I'm not sure I like my solution, there might be a better way.
>
> I also noticed another bug while looking at of_irq_parse_pci().  It returns
> the non-zero return value from pci_read_config_byte().  But that value is
> one of the PCI function error values from include/linux/pci.h, such as:
>
>     #define PCIBIOS_BAD_REGISTER_NUMBER     0x87
>
> instead of a negative errno.
>
>
> -Frank

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